Vis enkel innførsel

dc.contributor.authorDinamarca, Carlos S.nb_NO
dc.date.accessioned2014-12-19T13:11:02Z
dc.date.available2014-12-19T13:11:02Z
dc.date.created2010-11-03nb_NO
dc.date.issued2010nb_NO
dc.identifier360462nb_NO
dc.identifier.isbn978-82-471-2339-3 (printed ver.)nb_NO
dc.identifier.urihttp://hdl.handle.net/11250/244555
dc.description.abstractHydrogen gas generation has been studied by environmental biotechnologists since the 1930’s as a key intermediate in biogas process, and since the 70’s also because of its potential as a future energy carrier. Exhaustive studies on a variety of parameters that affect hydrogen production in fermentative processes have been published. Parameters studied include: pH, H2 and CO2, partial pressure, hydraulic retention time, feed and organic loads, nutrients, minerals, buffers systems and reactor configurations. Nevertheless, low hydrogen yields compared to the theoretical potential are often reported. (Article 1) Studies on hydrogen production by mixed cultures in series of batch and continuous flow reactors operated at various conditions, with glucose as the organic source, are presented in this dissertation. Batch tests, at different start pH, showed expected H2 production rates and yields. The produced hydrogen corresponded to the stoichiometry of the other products formed; mainly acetic and butyric acids. Continuous flow reactors had similar initial behavior, with hydrogen yields between 0.8 to 1.5 mol H2/mol glucose and about 50 % hydrogen in the headspace biogas. A decrease in the H2 production was, however, observed as cultures matured, resulting in hydrogen yields down to 0.02 mol H2/mol glucose. Molecular hydrogen consumption and/or equivalents hydrogen consumption was then hypothesized. (Article 2) Series of batch experiments where setup to study the ability of heat treated anaerobic sludge to consume molecular H2 in the absence of an organic electron source. Hydrogen consumption rates between 4 to 62 mmol H2/L sludge_d were found. The consumption rate was clearly affected by acetic acid concentration, headspace H2 partial pressure, and mass transfer phenomena. The observations suggested that juxtapositioned cells, hydrogen producer and consumers, can significantly increase the production and consumption rates by syntrophic associations similar to those described for hydrogenotrophic methanogens and acetogens. (Article 3) Simultaneous H2 production and consumption is however not obviously important because homoacetogenic bacteria hold both heterotrophic and autotrophic metabolic capabilities. Such microorganisms obtain much more energy and higher growth rates as heterotrophs than as autotrophs. This has been used as the main argument in the literature to defend the hypothesis that H2 consumption is irrelevant in bio-hydrogen mixed fermentation processes. Demonstrating clearly that H2 consumption is relevant in bio-hydrogen mixed fermentation processes was therefore given high priority in this study. The simultaneous activity of H2 producers (fermentative bacteria) and H2 consumers (homoacetogens) was also investigated in an upflow hybrid reactor run for 167 days. The reactor was run at a constant 30 hours HRT the first 93 days. HRT was then gradually decreased to achieve higher organic loads. Initial high H2 production similar to that observed in the batch experiments was observed during the startup period. This was gradually replaced by low hydrogen yield, equivalent to 0.02-0.4 mol H2/ mol glucose consumed. The distribution of the dissolved products was influenced strongly by reactor pH, while the gas production rate and composition was not. At low pH (<4.5) lactate fermentation was favored, while butyrate and acetate were the predominant products for pH of 5.0-5.5. Evidence of simultaneous hydrogen production and consumption were found. At least 22 % of the produced molecular hydrogen, mainly from butyrate fermentation, was used for the reduction of CO2 to acetate. Low hydrogen yield was observed even at high organic load operation when just about 45 % of the glucose added was consumed. H2 yield of 0.4 mol H2/mol glucose showed that highly packed (high biomass density) reactors without organic feed limitation can continuously consume hydrogen, presumably because of the establishment of micro-environments where homoacetogenic cells are exposed to higher H2 concentration than in the bulk phase and without access to organic feed. These results support the proposed (Article 3) existence of niches where juxtapositioned hydrogen producer and consumers establish conditions where homoacetogens rely on autotrophic metabolism. (Article 4) Environmental biotechnologies are generally based on the use of mixed cultures. Mixed cultures have a wide range of environmental and industrial applications, such as in the production of biofuels and bioplastics. Models are used as fundamental or process tools for the estimation of products distribution in fermentation processes and design of process plants. Standard fermentation models available today do not include hydrogen consumption processes. The results in the present thesis demonstrate the relevance of the inclusion of such processes, especially homoacetogenesis. H2 consumers, in non-methanogenic environments, will define the hydrogen partial pressure and therefore the redox state of the system, and consequently, the product distribution. (Article 5) &nbsp; &nbsp; &nbsp;&nbsp; &nbsp;nb_NO
dc.languageengnb_NO
dc.publisherTapir Uttrykknb_NO
dc.relation.ispartofseriesDoktoravhandlinger ved NTNU, 1503-8181; 2010:182nb_NO
dc.titleHomoacetogenic H2 Consumption In Fermentative Hydrogen Production Processesnb_NO
dc.typeDoctoral thesisnb_NO
dc.contributor.departmentNorges teknisk-naturvitenskapelige universitet, Fakultet for naturvitenskap og teknologinb_NO
dc.description.degreePhD i bioteknologinb_NO
dc.description.degreePhD in Biotechnologyen_GB


Tilhørende fil(er)

Thumbnail

Denne innførselen finnes i følgende samling(er)

Vis enkel innførsel